Is/Does the file exists?

Are/Do aliens exist?

I think I should use do, but there is some case I should use is? Also, does that mean something if I use is?

  • In your first sentence, regardless of the verb at beginning, the last word should be exist, not "exists". In interrogative form, the bare infinitive is always used, rather than conjugating the verb.. Jun 1 '15 at 6:32
  • If you wanted to use is, you'd word it with a "there", like this: Is there a file? Are there aliens?
    – J.R.
    Jun 1 '15 at 9:02

Sometimes it is helpful to try phrasing the question to an answer like this, and it may become clearer:

is/does the file exist? The file does exist.

are/do aliens exist? Aliens do exist.

If it sounds correct in the answer, that's the word to use in the question.

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